1. Field of Invention
The present invention relates to a high-speed electric spindle, and more particularly to an oil-mist-free and high-speed electric spindle in a bearing processing industry.
2. Description of Related Arts
An electric spindle, which is a short name of a high frequency spindle, is sometimes called a direct drive spindle as well. The electric spindle is a spindle unit of a built-in motor. The electric spindle shortens the length of a main transmission chain of a machine tool to zero, and accomplishes a result of “zero transmission” of the machine tool. The electric spindle has advantages of compact structure, high mechanical efficiency, availability of extremely high rotating speed, high rotating accuracy, low noise, small oscillation, and etc. Thus, the electric spindle is more and more widely used in a modern machine tool, especially a numerical control machine tool. And the electric spindle is particularly commonly applied to a bearing manufacturing industry.
Depending on the rotating speed of a spindle, electric spindles are classified as a low-speed electric spindle and a high-speed electric spindle. The high-speed electric spindle generally refers to the electric spindle with a bearing whose DN value reaches to 1˜2 million thereof. Since a spindle bearing of the high-speed electric spindle is in a sharply high-speed friction condition, and withstands a high temperature and high load, the lubrication thereof is very important.
The high-speed electric spindle produces large amounts of heat while in operation, which causes a temperature rising thereof. Thus, unlike the low-speed electric spindle, the high-speed spindle does not use a grease lubrication, but an oil-mist lubrication, an oil-air lubrication or a spray lubrication. That is because in the grease lubrication, the grease is not capable of being maintained in the bearing. The so called oil-mist lubrication means using a compressed air which is purified to spray a dedicated oil into a mist condition via a dedicated spraying device; and using the compressed air to forcefully put the oil mist into the bearing portion of the electric spindle so as to lubricate the high-speed bearing. While using the oil-mist lubrication for lubricating, a manufacture of the compressed air consumes huge energy. And each electric spindle on average requires being equipped with an air compressor of 2˜2.5 kw, which consumes a lot of power; and each electric spindle on average requires 1˜2 kg spindle dedicated oil, which consumes a lot of oil. Furthermore, in the oil-mist lubrication mode, the oil mist is instantly discharged into the air after passing through the bearing of the electric spindle, which causes a serious environmental pollution and harms a physical condition of the employee as well.
On the other hand, because a rotating speed of the high-speed electric spindle reaches to sixty thousands per minute or more, and a DN value of the bearing reaches to 1˜2 million, it is not possible to use a contact sealing structure. For example, while applying the conventional electric spindle which uses non-contact seal structure to a bearing grinder, if a mist-and-air lubrication is closed, there is no positive-pressure compressed air in the electric spindle. The operating of the bearing grinder is coupled with a spraying or sputtering of plentiful coolant which contains grinding iron filings, threshings of a grinding wheel and sundries that are capable of entering into the bearing of the electric spindle, so a force exerted on the bearing varies, which causes problems that the spindle generates abnormal sounds or even stops rotating, so that a motor coil is burnt out. When using a liquid coolant, the harm is more serious.
At the same time, as the non-contact sealing structure uses a gas or liquid tension between two surfaces to achieve a sealing effect, a space of two relatively moving elements must be controlled in a certain range. If the space is too small, a slight impact in operation damages the bearing easily; and if the space is too large, the sealing is ineffective.